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Given below are some elements of the modern periodic table. Atomic number of the element is given in the parentheses : A(4), B(9), C(14), D(19), E(20) (a)

Select the element that has one electron in the outermost shell, Also write the electronic configuration of this element. (b) Which two elements amongst these belong to the same group ? Give reason for your answer. (c) Which two elements amongst these belong to the same period ? Which one of the two has bigger atomic radius?


A) D(19),(2,8,8,1)
B)A AND E (Both have same number of valence electrons in the last shell that is 2) A=(2,2) ,E=(2,8,8,2)
C)A AND B are of same period( second period)
   D AND E also(third period)
A has more atomic radius than B
E has more atomic radius than D ( Electrons are added in the same shell,the nuclear power increases and attracts electrons closer to it.So from going left to right in periodic table atomic radius of mass decreases)

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(a) Element D (2 8 8 1)
(b) Elements A& E because they have 2 electrons in their outermost shell
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